Re: Recover preallocated space after a crash?

[Gionatan Danti <g.danti@assyoma.it>]

Il 2020-11-07 21:47 Dave Chinner ha scritto:
> On Sat, Nov 07, 2020 at 08:55:50PM +0100, Gionatan Danti wrote:
>> Hi list,
>> it is my understanding that XFS can preallocate some "extra" space via
>> speculative EOF preallocation and speculative COW preallocation.
>> 
>> During normal system operation, that extra space is recovered after 
>> some
>> time. But what if system crashes? Can it be even recovered? If so, it 
>> is
>> done at mount time or via a (more invasive) fsck?
> 
> It will be done silently the next time the inode is cycled through
> memory via an open()/close() pair as specualtive prealloc is removed
> on the final close() of a file.
> 
> Alternatively, you can trigger reclaim on the current set of
> in-memory inodes by running:
> 
> # xfs_spaceman -c "prealloc -m 64k -s" /mnt
> 
> to remove speculative preallocations of more than 64k from all
> inodes that are in-memory and wait for the operation to complete.
> 
> You still need to bring the inodes into memory, so you can do this
> via find command that reads some inode metadata (e.g. find /mnt
> -ctime 2>&1 /dev/null). This means you don't need to actually
> open/close each inode in userspace - the filesystem will traversal
> all the in-memory inodes and clear the prealloc space itself.
> 
> Cheers,
> 
> Dave.

Hi Dave,
thanks so much for the clear answer.

-- 
Danti Gionatan
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